1. Field of the Invention
The present invention relates to generators and, more specifically, to a system for generating voltage and current using the triboelectric effect.
2. Description of the Related Art
Energy harvesting by converting ambient energy into electricity may offset the reliance of small portable electronics on traditional power supplies, such as batteries. When long-term operation of a large number of electronic devices in dispersed locations is required, energy harvesting has the advantages of outstanding longevity, relatively little maintenance, minimal disposal and contamination.
When two materials, at least one of which is non-conducting, come into contact with each other, a chemical bond, known as adhesion, is formed between the two materials. Depending on the triboelectric properties of the materials, one material may “capture” some of the electrons from the other material. If the two materials are separated from each other, a charge imbalance will occur. The material that captured the electron will negatively charged and the material that lost an electron will be positively charged. This charge imbalance gives rise to what is sometimes referred to as “static electricity.” The term “static” in this case is somewhat deceptive, as it implies a lack of motion when in reality motion is necessary for charge imbalances to flow. The spark one feels upon touching a door knob is an example of such flow.
The triboelectric effect is a type of contact electrification in which certain materials become electrically charged after they come into contact with another such as through friction. It is the mechanism though which static electricity is generated. The triboelectric effects associated electrostatic phenomena are the most common electrical phenomena in daily life, from walking to driving. However, the triboelectric effect has been largely ignored as an energy source for electricity. Some electrostatic micro-generators have been developed and used in research relating to micro-electro-mechanical systems (MEMS), but such designs rely on an extra voltage source to charge electrode plates instead of harnessing triboelectric effect, leading to complicated structures and fabrication processes.
Previously demonstrated triboelectric generators require periodic contact and vertical separation of two materials that have opposite triboelectric polarities, making it only applicable to harvest energy from intermittent impact or shock. Such systems typically include a cavity with a constantly changing volume, which makes packaging difficult and limits applications in atmospheres with high humidity, corrosive chemicals or gases, and in water or other liquids.
Mechanisms using piezoelectric, electrostatic or electromagnetic principles to harvest energy from random vibrations, wind flow, air pressure, or human body motions have been developed and applied as generators or self-powered sensors. Recently, the development of triboelectric nanogenerators (triboelectric generators) offers a new paradigm for fabricating high-output and cost effective generators for driving small electronics. Reciprocating motion is a very common mechanical motion occurs in natural oscillations, motion of waves, swing of human limbs, and mechanical piston movements, etc. Features of these motions that include long reciprocating distance, low frequencies and amplitude or frequency fluctuations pose challenges for previously developed vibration-harvesters, which were only suited to low-amplitude and high-frequency excitations induced by inertia forces.
Therefore, there is a need for a reliable, small and easily manufactured system for harvesting triboelectric energy from reciprocating motion.